"I didn't think that another pregnancy was possible," Maci told In Touch Weekly. After being diagnosed with polycystic ovary syndrome (PCOS) following the birth of her now 6-year-old son Bentley, Maci thought that it would be impossible for her to give her son a sibling.
Maci revealed that she found out she was pregnant after she went to the doctor for "very strange symptoms."
"My legs were very itchy and I had tenderness in my breasts. So we got a test and it said I was pregnant," Maci told the magazine.
The young mother and her boyfriend of two years, Taylor McKinney, were thrilled with the news.
"We still can't believe it," Maci told In Touch. "It was a huge shock, but we are very excited."
Maci, described by MTV as an "overachiever," split from Bentley's father, Ryan, after the first season of "Teen Mom." She told the Associated Press that she originally participated in the show in 2009 to give a positive message to girls like her.
"I really just wanted to show girls how hard it was to be a teen parent," she said. "I wanted girls who might get pregnant to see there are options out there to move forward with your life and still have goals."
Now, Maci is a college student, majoring in journalism, and speaks at high schools about teen pregnancy.
Last year, she opened up about another health scare last year on "The Doctors." Maci was plagued by a mysterious illness, which turned out to be a kidney infection that gave her a pain far worse than even childbirth.
"Oh my God, I'd rather have eight kids at once than do that!" Maci said.